The present invention relates generally to compositions comprising limestone and clay, and more particularly to such compositions which are used as a traction aid for streets and sidewalks when covered with ice or snow.
Various materials have been used in the past to improve traction on otherwise slippery surfaces. It has been particularly important to use such materials to improve traction on streets and sidewalks when covered with ice or snow. A common material for this use has been sand. During ice or snow conditions, it has been a common practice to spread sand over streets by truck or over sidewalks by hand to thereby mechanically improve traction by providing the surface with increased roughness. However, one problem with using sand for this purpose has been its relatively small particle size. That is, because the grains of sand are so small, they are more readily compacted into the ice or snow to the extent that they no longer project above the surface of the ice or snow whereby their traction enhancement is lost. This small particle size also allows the sand to be more easily blown by wind off of the surface to which it was applied. Another problem with using sand has been its relatively high density. Because sand is so dense, it takes a relatively large weight of it to cover a certain surface area.
Another type of material which has been commonly used is inorganic salt. such as sodium chloride or calcium chloride. These salts. which have been applied in the same way as sand, have been particularly useful because of the effect they have in melting the ice or snow. Salts have therefore become widely used by street departments and homeowners alike. However, certain problems and limitation exist with using salt. The most serious problem is the harmful effects the salt has on the environment. It is well-known that salt applied to the road causes cars to rust at a faster rate. In addition, the salt causes increased rusting of the reinforcing and other structural steel used in highway construction. Also, because the salt is so highly water soluble, it is rather mobile and is washed into the adjacent fields and eventually into the area's entire water system thereby creating serious problems for people, plants and animals.
Another drawback of using salt for traction enhancement is the fact that its effectiveness is pretty much limited to its chemical action of melting the ice or snow. That is, the salt does not provide much mechanical traction enhancement because it is so easily dissolved in water and so easily crushed. Yet another limitation of using salt is the fact that below a certain temperature, it will not melt ice or snow, causing a freeze-thaw cycle that further erodes porous road surfaces through a process known as spalling.